a) Field of the Invention
The invention relates to a seal arrangement for a load-carrying bearing which is supported on a guide path provided on a carrying body and which is arranged so as to be movable along the length of the guide path, especially for coordinate measuring devices.
b) Description of the Related Art
Load-carrying bearings which are supported on guide paths that are arranged on carrying bodies and which are movable along these guide paths are used in many areas of technology, e.g., for supporting movable machine tables for machine tools or as supporting bearings for bridges or portals in coordinate measuring devices.
The simplest construction of bearings of the type mentioned above consists in that the bearing in question is only supported so as to be movable on the associated guide path without any special sealing devices being provided in order to prevent penetration by dirt, floating particles, aerosols, moisture, or the like, into the bearing surface. Such arrangements are possible when requirements with respect to the insensitivity of the guide elements to dirt are relatively undemanding or when the device in question operates in a suitable cleanroom.
However, devices of the type mentioned above are increasingly used in manufacturing environments, i.e., the machines are no longer set up in closed, air-conditioned rooms and halls which are protected from access by manufacturing media, but rather in rooms and halls used for manufacturing, so that there is a risk that all of the contaminants and the like which are present in such manufacturing halls will lead to impairment of the guide paths and therefore to impaired quality of the bearing surfaces. This is especially undesirable when the machines in question are high-precision measurement devices in which such influences must be eliminated.
Accordingly, a seal arrangement has already been provided in coordinate measuring devices for sealing bearings of the kind mentioned above. In this seal arrangement, the guide path and the bearing supported on the guide path are covered by a box-shaped cover plate, on whose side opposite to the guide path is formed a central longitudinal slot through which is guided a connection element which connects the bearing with a structure to be supported located outside of the cover plate. Within the space enclosed by the cover plate, near the longitudinal slot, this connection element has a wide guide body which extends on both sides along the lateral edges of the longitudinal slot and which (seen in the longitudinal direction of the longitudinal slot) is penetrated by a through-opening. A cover strip, whose shape is adapted to the through-opening and which extends inside the cover plate along its entire length, runs through this through-opening and serves to cover the longitudinal slot on the inner side of the cover plate. This cover strip, whose width also projects over the sides of the longitudinal slot, is fastened in a suitable manner at both of its ends. Since the cover strip runs through the through-opening of the guide body, the bearing can be moved along the strip with the connection element coupled to it and the structure to be supported which is connected with the latter, so that the longitudinal movement required for the bearing is ensured, but the cover strip still conceals the open longitudinal slot opposite to the inner side of the cover plate at all times in the areas outside of the bearing. Since the cover strip is arranged at a distance from the longitudinal slot of the cover plate because of the overall construction, even though this distance is only slight, a certain sealing can accordingly be provided against penetration of dirt, dust and the like, but the existing gaps are relatively large, so that there is still no guarantee of a particularly good sealing action against contamination of the guide elements or penetration of floating particles.
In another known structural solution, a bellows is connected to each side of the bearing (in its movement direction) and, as seal protection, covers the portion of the guide path on the bearing side that is not covered by the bearing. However, the cost of the encapsulation required for this purpose by means of the bellows over the entire length and width of the guide surface is considerable, and the forces to be applied for the displacement of the bellows are not conducive to the absence of forces which is desired as far as possible in the longitudinal displacement of the utilized bearing.
On this basis, the primary object of the invention is to provide an improved seal arrangement which ensures a particularly low susceptibility on the part of the guide elements to soiling and improved protection against the penetration of floating particles, aerosols and moisture while simultaneously providing a good overall static and dynamic characteristic of the moving system.
According to the invention, this object is achieved in a seal arrangement of the type mentioned above in that the bearing is connected with a bearing cover that spans the carrying body at least on one side thereof and that has a side portion which is bent toward its side, each side portion projecting into a labyrinth recess which is arranged on the associated side of the carrying body over the entire length of the guide path to form a labyrinth seal.
The seal arrangement proposed according to the invention results in a remarkably good sealing of the bearing relative to the external surroundings in which a manufacturing atmosphere exists, and even exacting guideline values concerning insensitivity to soiling can easily be met. At the same time, a superior protection is provided against the penetration of floating particles, aerosols and moisture and the overall construction also leads to good static and dynamic overall characteristics of the moving bearing system.
The sealing arrangement according to the invention can also easily be varied with respect to installation position: installation can accordingly be carried out vertically, horizontally or in some other defined position without substantially impairing the sealing action. At the same time, the sealing arrangement according to the invention also allows an economical configuration with a modular construction in the manner of a building block system; such modular components for a building block system are, for example, the bearing cover with its side portions which are bent at both sides and the body forming the labyrinth recess, along with the carrying body with guide path and the bearing itself.
The seal arrangement according to the invention also has a total configuration with easily assembled and service-friendly joints, which is especially advantageous for cleaning within regulation maintenance intervals.
If floating particles and aerosols enter the labyrinth seal from outside the bearing in the sealing arrangement according to the invention, they are slowed down with respect to flow velocity on their way through the labyrinth seal already in the first arm of the labyrinth, so that the heavier particles settle on the bottom of the labyrinth recess during the following labyrinth deflection and when entering the other labyrinth arm running in the opposite direction. This effect is particularly important when the seal arrangement according to the invention is installed in such a way that the labyrinth channels extend substantially vertically, so that the gravitational force within the latter also acts on the entering dirt particles in the same direction. In connection with the 180-degree deflection of the labyrinth channels, the precipitating effect of dirt or residual dirt is very good. The very long and very narrow winding flow channels within the labyrinth seal not only provide for an extremely long flow path, but also for a strong deceleration of the occurring flow velocities, especially with respect to the very narrow channel cross sections in which there are considerable wall friction losses in the case of a gas flowing therein.
A particular advantage of the sealing arrangement according to the invention also consists in that it works in an entirely contact-free manner and no additional expenditure of force is required apart from the force required for the displacement of the bearing during a movement of the bearing. The seal arrangement according to the invention can be assembled and disassembled comparatively quickly, which is especially advantageous when carrying out maintenance work. In addition, dirt and dust particles or the like which may have settled in the winding paths of the labyrinth seal can also be removed quickly and easily after disassembling.
A particularly advantageous construction of the seal arrangement according to the invention consists in that the utilized bearing is constructed as an air bearing. In this way, a bearing/seal unit working in a noncontacting manner can be produced, which is particularly advantageous precisely with machines such as coordinate measuring devices which operate with very high precision because no friction forces need to be overcome in the adjusting movement in spite of the seal. In cases where this aspect is not so important, the utilized bearing can, of course, also easily be constructed in any other suitable form of bearing, e.g., as a rolling bearing or in exceptional cases even as a sliding bearing.
In another advantageous construction of the invention, the side surfaces of the carrying body on which the guide path is arranged and the bent side portion(s) of the bearing cover extend(s) essentially at right angles to the surface of the guide path. The space requirement for the seal arrangement according to the invention lateral to the course of the guide path is minimized in this way. However, in special cases of use it can also be advantageous when the side surfaces of the carrying body extend diagonally and not at right angles to the plane of the guide path, in which case the bent side portion(s) of the bearing cover should also preferably have a corresponding alignment.
An especially advantageous and effective construction of the seal arrangement according to the invention can be achieved in that the bent side portion, or every bent side portion, of the bearing cover has a construction that is U-shaped in cross section by which it projects into the associated labyrinth recess, wherein the arrangement is preferably carried out in such a way that the closed end of the U-shaped cross section of a side portion of this type is located inside of the labyrinth seal, i.e., the open side of the U-shaped cross section is directed out of the labyrinth recess. Since a U-shaped side leg projects into the U-shaped labyrinth recess in this case, a particularly long flow path is achieved inside the labyrinth seal and a right-angle deflection therefore takes place twice, namely, at the two end edges of the middle leg of the U-shaped side portion. In this case, a dirt precipitation area is created within the winding course of the flow cross section in this labyrinth seal between the two middle legs of the two U-shaped cross sections which are located one inside the other, wherein, in another preferred embodiment of the invention in which the labyrinth channels extend essentially vertically outside of the cleaning area, all of the heavier particles can settle specifically in this dirt precipitation area due to the gravitational force acting on the particles in the channels in addition to the deflection. This enables a simple and fast cleaning for maintenance purposes, wherein the bottoms of the labyrinth recess in all areas lying outside of the precise location of the bearing are easily accessible.
When the bent side portion(s) also has/have a construction which is U-shaped in cross section and lies/lie with the middle web of its/their U-shaped cross section in the labyrinth recess, another especially preferred construction of the invention consists in that the guide path is covered along its entire length by a guide path cover which is U-shaped in cross section and which likewise covers the bearing cover and its side portion(s) and projects into the recess of the U-shaped cross section of the associated side portion of the bearing cover in the area of the bearing with its side leg or with each of their side legs, wherein the lateral outside leg of the U-shaped cross section of the side portion or of each side portion is lengthened beyond the level of the position of the middle leg of the U-shaped guide path cover and is connected in that location with a structure which is to be supported by the bearing. This results in a construction of the sealing arrangement according to the invention which, in addition to a superior sealing action in spite of the guide path cover completely covering the guide path and in spite of the arrangement of the bearing inside of the area covered by the guide path cover, makes possible a problem-free supporting of the structure (such as a bridge or a portal of a coordinate measuring device) which is to be supported and which is located outside of the seal arrangement. In this advantageous construction of the invention, the forces to be supported via the bearing by the structure to be supported are transmitted to this bearing in such a way that the bearing cover is used as a force-transmitting element between them which, due to its U-shaped construction, can engage around the lower ends of the guide path cover so as to reach the inner side of the guide path cover from its outer side and accordingly so as to produce a connection from the outside supported structure to the bearing. The various parts which engage one inside the other act together to effect an excellent sealing toward the outside; at the same time, because of the selected shape of the guide path cover, it is possible for force to be transmitted from the structure to be supported which is located outside of the guide path cover to the supporting bearing inside of the guide path cover without problems. Particularly remarkable in this respect is the constructive method used for this purpose which consists in simultaneously using the bearing cover as a connection part for transmitting forces toward the structure to be supported, apart from its function for covering and forming the labyrinth seal.
The labyrinth recesses can be formed or arranged in any suitable manner at the carrying body lateral to the guide path. However, it is especially preferable that every labyrinth recess is formed of a shaped section which is arranged at the side of the carrying body and which is advantageously attached to a machine base body to which the carrying body can also be attached simultaneously. In this way, a fixed connection is provided between the shaped section and the carrying body, but without the two parts being fastened to one another directly, so that, if necessary, the shaped section can also be modified with respect to its orientation relative to the carrying body during assembly.
In the embodiments of the seal arrangement according to the invention which were described above, it is especially preferable that the labyrinth recess formed by the shaped section is lengthened on its side remote of the carrying body beyond the free end of the outside leg of the side portion engaging therein, specifically, to the extent that it projects beyond the fastening point between the side portion and the structure to be supported and is provided at its end with an end region which is bent toward the structure to be supported by the bearing. When this end region projects far enough to reach into the vicinity of the sides of the structure to be supported which face it, but does not touch these sides, yet another covering can be achieved in the bearing portion above the location where the structure to be supported is fastened to the outside leg of the side portion of the bearing cover, so that the sealing action of the seal arrangement is further improved.
Like the shaped section for forming the labyrinth recess, the bearing cover can likewise be constructed in any suitable shape and can also be formed from a plurality of individual parts which are connected with one another. It is particularly preferable, however, when the bearing cover with its side portion(s) and/or the shaped section are formed in one piece from a sheet metal shape which can then also be used as a modular structural component and can be produced in a comparatively simple manner. In this way, assembly is also facilitated on the whole and, particularly with the one-piece construction of the bearing cover with the side portion(s), a particularly good transmission of force is achieved between the bearing and the structure to be supported.
Another preferred construction of the sealing arrangement according to the invention also consists in that the shaped section forming the labyrinth recess has, on its side facing the carrying body, a side leg which is essentially parallel to the side surface of the carrying body and which extends in the direction of the guide path but ends at a distance before the position level of the latter, wherein, likewise preferably, the shaped section contacts the side surface of the carrying body facing it by its side leg. In this way, even if a small portion of residual dirt should actually pass through the labyrinth channel formed between this side leg of the shaped section and the associated side portion of the bearing cover, it will settle behind it in the stretch of channel formed between the side surface of the carrying body and the side surface of the side portion of the bearing cover facing this first side surface (before reaching the surface of the carrying body on which the guide path is arranged) and can therefore not even reach the guide path.
In the following, the invention will be described in principle more fully by way of example with reference to the drawings.